Mini-bows and Droplet Shape

Rays passing through a single drop on a blade of grass can show effects other than the classical rainbow because of slight distortions in the drop shape. Although most of the colour is found close to the rainbow angles it is worth exploring other angles to find features caused by the distorted drops.

Rainbow from an undistorted drop Undistorted droplet on grass

This typical bow above was formed by light passing through the undistorted part of the drop on the right. It shows the classic cutoff at the red edge and bright inner region where all the colours overlap.

Pure rainbow colours in a drop Distorted drop on grass

The path through the drop seems similar here but the rays emerge where the drop curvature is changing. The blue part of the bow isn't as diluted as the example above.

Strong supernumeraries from a droplet Small undistorted droplet

A strong set of supernumeraries from this smaller than average drop, which isn't obviously distorted.

Multiple supernumeraries from a droplet Small slightly distorted drop

A similar effect but the colours are more washed out here, possibly something to do with the change of curvature where the rays emerge from this small drop.

Canon EOS 20D   27th July 2008
Wiltshire, England

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